| Internet Engineering Task Force | V. Govindan |
| Internet-Draft | C. Pignataro |
| Updates: 5885 (if approved) | Cisco Systems |
| Intended status: Standards Track | August 12, 2015 |
| Expires: February 13, 2016 |
Seamless BFD for VCCV
draft-ietf-pals-seamless-vccv-00
This document extends the procedures and Connectivity Verification (CV) types already defined for Bidirectional Forwarding Detection (BFD) for Virtual Circuit Connectivity Verification (VCCV) to define Seamless BFD (S-BFD) for VCCV. This document will be extended in future to include definition of procedures for S-BFD over Tunnels. This document extends the CV values defined in RFC5885.
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This Internet-Draft will expire on February 13, 2016.
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BFD for VCCV [RFC5885] defines the CV types for BFD using VCCV, protocol operation and the required packet encapsulation formats. This document extends those procedures, CV type values to enable S-BFD [I-D.ietf-bfd-seamless-base] operation for VCCV.
The new S-BFD CV Types are PW demultiplexer-agnostic, and hence applicable for both MPLS and Layer Two Tunneling Protocol version 3 (L2TPv3) pseudowire demultiplexers. This document concerns itself with the S-BFD VCCV operation over single-segment pseudowires (SS-PWs). The scope of this document is as follows:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
S-BFD protocol provides continuity check services by monitoring the S-BFD control packets sent and received over the VCCV channel of the PW. The term <Connectivity Verification> is used throughout this document to be consistent with [RFC5885].
This section defines the CV types to be used for S-BFD. It also defines the procedures for S-BFD discriminator advertisement for the SBD reflector and the procedure for S-BFD Initiator operation.
Two CV Types are defined for S-BFD. Table 1 summarizes the S-BFD CV Types, grouping them by encapsulation (i.e., with versus without IP/UDP headers) for fault detection only. S-BFD for fault detection and status signaling is outside the scope of this specification.
| Fault Detection Only | Fault Detection and Status Signaling | |
|---|---|---|
| S-BFD, IP/UDP Encapsulation (with IP/UDP Headers) | TBD1 (Note1) | N/A |
| S-BFD, PW-ACH Encapsulation when using MPLS PW or L2SS Encapsulation when using L2TP PW (without IP/UDP Headers) | TBD2 (Note2) | N/A |
Two new bits are requested from IANA to indicate S-BFD operation.
Since the CV types for S-BFD and BFD are unique, BFD and S-BFD capabilities can be advertised concurrently.
The S-BFD Initiator SHOULD bootstrap S-BFD sessions after it learns the discriminator of the remote target identifier through one or more of the following methods:
S-BFD Initiator operation MUST be according to the specifications in Section 7.2 of [I-D.ietf-bfd-seamless-base].
TBD
The procedures of S-BFD Reflector described in [I-D.ietf-bfd-seamless-base] apply for S-BFD using VCCV.
TBD.
The S-BFD Reflector MUST use the AVP [I-D.ietf-l2tpext-sbfd-discriminator] defined for advertising its target discriminators using L2TP.
S-BFD target discriminators MAY be provisioned when static PWs are used.
S-BFD alert discriminators MAY be used to probe S-BFD target discriminators. If a node implements S-BFD reflector, it SHOULD respond to Alert discriminator requests received from potential S-BFD Initiators.
Unless specified differently below, the encapsulation of S-BFD packets is the identical the method specified in Sec.3.2 [RFC5885] and in [RFC5880] for the encapsulation of BFD packets.
When multiple S-BFD CV Types are advertised, and after applying the rules in [RFC5885], the set that both ends of the pseudowire have in common is determined. If the two ends have more than one S-BFD CV Type in common, the following list of S-BFD CV Types is considered in the order of the lowest list number CV Type to the highest list number CV Type, and the CV Type with the lowest list number is used:
The order of capability selection between S-BFD and BFD is defined as follows:
| Advertised capabilities of PE1/ PE2 | BFD Only | SBFD Only | Both S-BFD and BFD |
|---|---|---|---|
| BFD Only | BFD | None (Note1) | BFD Only |
| S-BFD Only | None (Note1) | S-BFD | S-BFD only |
| Both S-BFD and BFD | BFD only | S-BFD only | Both SBFD and BFD |
Note1: Can we mandate failing the bringup of the PW in case of a capability mismatch?
Security measures described in [RFC5885] and [I-D.ietf-bfd-seamless-base] are to be followed.
The VCCV Interface Parameters Sub-TLV codepoint is defined in [RFC4446], and the VCCV CV Types registry is defined in [RFC5085].
This section lists the new BFD CV Types.
IANA has augmented the "VCCV Connectivity Verification (CV) Types" registry in the Pseudowire Name Spaces reachable from [IANA]. These are bitfield values. CV Type values TBD are specified in Section 2 of this document.
MPLS Connectivity Verification (CV) Types:
Bit (Value) Description Reference
=========== =========== ==============
TBD1(0xY) S-BFD IP/UDP-encapsulated, this document
for PW Fault Detection only
TBD2(0xZ) S-BFD PW-ACH/L2SS-encapsulated, this document
for PW Fault Detection only
This section lists the new requests for S-BFD CV Types to be added to the existing "VCCV Capability AVP" registry in the L2TP name spaces. The Layer Two Tunneling Protocol "L2TP" Name Spaces are reachable from [IANA]. IANA is requested to assign the following L2TPv3 Connectivity Verification (CV) Types in the VCCV Capability AVP Values registry.
VCCV Capability AVP (Attribute Type 96) Values
----------------------------------------------
L2TPv3 Connectivity Verification (CV) Types:
Bit (Value) Description Reference
=========== =========== ==============
TBD1(0xY) S-BFD IP/UDP-encapsulated, this document
for PW Fault Detection only
TBD2(0xZ) S-BFD L2SS-encapsulated, this document
for PW Fault Detection only
As per the IANA considerations in [RFC5586], IANA is requested to allocate the following Channel Types in the "MPLS Generalized Associated Channel (G-ACh) Types" registry:
IANA has reserved a new Pseudowire Associated Channel Type value as follows:
Registry:
TLV
Value Description Follows Reference
------ ---------------------------------- ------- ---------------
TBD2 S-BFD Control, PW-ACH/L2SS No [This document]
encapsulation
(without IP/UDP Headers)
Authors would like to thank Nobo Akiya, Stewart Bryant, Pawel Sowinski and Greg Mirsky for providing the core inputs of this document and for performing thorough reviews and providing number of comments. Authors would also like to thank Yuanlong for comments received.
Mallik Mudigonda
Cisco Systems
Email: mmudigon@cisco.com
| [IANA] | Internet Assigned Numbers Authority, "Protocol Registries" |